U.S. patent application number 16/566626 was filed with the patent office on 2020-01-02 for imaging lens and imaging apparatus.
This patent application is currently assigned to FUJIFILM Corporation. The applicant listed for this patent is FUJIFILM Corporation. Invention is credited to Kazuyoshi OKADA.
Application Number | 20200003991 16/566626 |
Document ID | / |
Family ID | 63523084 |
Filed Date | 2020-01-02 |
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United States Patent
Application |
20200003991 |
Kind Code |
A1 |
OKADA; Kazuyoshi |
January 2, 2020 |
IMAGING LENS AND IMAGING APPARATUS
Abstract
The imaging lens consists of, in order from the object side, a
positive first lens group that moves to the object side during
focusing from a long distance to a short distance, and a second
lens group that does not move during focusing. The first lens group
has a first-B sub-lens group. The first-B sub-lens group consists
of, in order from the object side, a positive b1 lens, a negative
b2 lens concave toward the image side, an aperture stop, a negative
b3 lens concave toward the object side, and a positive b4 lens. The
second lens group consists of, in order from the object side, a
negative lens, a positive lens, and a negative lens. Predetermined
conditional expressions are satisfied.
Inventors: |
OKADA; Kazuyoshi; (Saitama,
JP) |
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Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
FUJIFILM Corporation
Tokyo
JP
|
Family ID: |
63523084 |
Appl. No.: |
16/566626 |
Filed: |
September 10, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2018/008425 |
Mar 5, 2018 |
|
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16566626 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 13/02 20130101;
G02B 13/18 20130101; G02B 13/24 20130101; G02B 9/10 20130101; G02B
9/64 20130101 |
International
Class: |
G02B 9/10 20060101
G02B009/10; G02B 13/02 20060101 G02B013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2017 |
JP |
2017-049840 |
Claims
1. An imaging lens consisting of, in order from an object side: a
first lens group that moves toward the object side during focusing
from a distant object to a close-range object and has a positive
refractive power; and a second lens group that remains stationary
with respect to an image plane during focusing, wherein the first
lens group has a first-B sub-lens group including an aperture stop
in an inside thereof, wherein the first-B sub-lens group consists
of, in order from the object side, a b1 lens which is a positive
lens, a b2 lens which is a negative lens concave toward an image
side, an aperture stop, a b3 lens which is a negative lens concave
toward the object side, and a b4 lens which is a positive lens,
wherein the second lens group consists of, in order from the object
side, a negative lens, a positive lens, and a negative lens, and
wherein assuming that a distance on an optical axis from an object
side surface of the b1 lens to an image side surface of the b2 lens
is Db12, a distance on the optical axis from a surface closest to
the object side in the first lens group to a surface closest to the
image side in the first lens group is DG1, a maximum image height
is Ymax, a total number of lens surfaces of the second lens group
is k, a refractive index of a medium, which forms an i-th lens
surface from the object side in the second lens group, on the
object side at a d line is Nif, a refractive index of the medium,
which forms the i-th lens surface from the object side in the
second lens group, on the image side at the d line is Nir, a radius
of curvature of the i-th lens surface from the object side in the
second lens group is sRi, a radius of curvature of the image side
surface of the b2 lens is Rb2r, and a radius of curvature of an
object side surface of the b3 lens is Rb3f, Conditional Expressions
(1), (2) and (3) are satisfied, which are represented by 0.1 <
Db 12 / DG 1 < 0.25 , ( 1 ) - 0.02 < Y max .times. i = 1 k (
1 Nif - 1 Nir ) / sRi < 0.08 , and ( 2 ) - 0.3 < ( Rb 2 r +
Rb 3 f ) / ( Rb 2 r - Rb 3 f ) < 0.3 . ( 3 ) ##EQU00006##
2. An imaging lens consisting of, in order from an object side: a
first lens group that moves toward the object side during focusing
from a distant object to a close-range object and has a positive
refractive power; and a second lens group that remains stationary
with respect to an image plane during focusing, wherein the first
lens group has a first-B sub-lens group including an aperture stop
in an inside thereof, wherein the first-B sub-lens group consists
of, in order from the object side, a b1 lens which is a positive
lens, a b2 lens which is a negative lens concave toward an image
side, an aperture stop, a b3 lens which is a negative lens concave
toward the object side, and a b4 lens which is a positive lens,
wherein the second lens group consists of, in order from the object
side, a negative lens, a positive lens, and a negative lens, and
wherein assuming that a distance on an optical axis from an object
side surface of the b1 lens to an image side surface of the b2 lens
is Db12, a distance on the optical axis from a surface closest to
the object side in the first lens group to a surface closest to the
image side in the first lens group is DG1, a maximum image height
is Ymax, a total number of lens surfaces of the second lens group
is k, a refractive index of a medium, which forms an i-th lens
surface from the object side in the second lens group, on the
object side at a d line is Nif, a refractive index of the medium,
which forms the i-th lens surface from the object side in the
second lens group, on the image side at the d line is Nir, a radius
of curvature of the i-th lens surface from the object side in the
second lens group is sRi, a radius of curvature of an object side
surface of the b3 lens is Rb3f, and a radius of curvature of an
image side surface of the b3 lens is Rb3r, Conditional Expressions
(1), (2) and (6) are satisfied, which are represented by 0.1 <
Db 12 / DG 1 < 0.25 , and ( 1 ) - 0.02 < Y max .times. i = 1
k ( 1 Nif - 1 Nir ) / sRi < 0.08 , and ( 2 ) - 0.8 < ( Rb 3 f
+ Rb 3 r ) / ( Rb 3 f - Rb 3 r ) < 0. ( 6 ) ##EQU00007##
3. An imaging lens consisting of, in order from an object side: a
first lens group that moves toward the object side during focusing
from a distant object to a close-range object and has a positive
refractive power; and a second lens group that remains stationary
with respect to an image plane during focusing, wherein the first
lens group has a first-B sub-lens group including an aperture stop
in an inside thereof, wherein the first-B sub-lens group consists
of, in order from the object side, a b1 lens which is a positive
lens, a b2 lens which is a negative lens concave toward an image
side, an aperture stop, a b3 lens which is a negative lens concave
toward the object side, and a b4 lens which is a positive lens,
wherein the second lens group consists of, in order from the object
side, a negative lens, a positive lens, and a negative lens, and
wherein assuming that a distance on an optical axis from an object
side surface of the b1 lens to an image side surface of the b2 lens
is Db12, a distance on the optical axis from a surface closest to
the object side in the first lens group to a surface closest to the
image side in the first lens group is DG1, a maximum image height
is Ymax, a total number of lens surfaces of the second lens group
is k, a refractive index of a medium, which forms an i-th lens
surface from the object side in the second lens group, on the
object side at a d line is Nif, a refractive index of the medium,
which forms the i-th lens surface from the object side in the
second lens group, on the image side at the d line is Nir, a radius
of curvature of the i-th lens surface from the object side in the
second lens group is sRi, a radius of curvature of an object side
surface of the b2 lens is Rb2f, and a radius of curvature of the
image side surface of the b2 lens is Rb2r, Conditional Expressions
(1), (2) and (7) are satisfied, which are represented by 0.1 <
Db 12 / DG 1 < 0.25 , and ( 1 ) - 0.02 < Y max .times. i = 1
k ( 1 Nif - 1 Nir ) / sRi < 0.08 , and ( 2 ) 0.3 < ( Rb 2 f +
Rb 2 r ) / ( Rb 2 f - Rb 2 r ) < 1.5 . ( 7 ) ##EQU00008##
4. The imaging lens according to claim 1, wherein assuming that a
focal length of the imaging lens during focusing on an object at
infinity is f, and a focal length of the second lens group is f2,
Conditional Expression (4) is satisfied, which is represented by
-0.7<f/f2<0.3 (4).
5. The imaging lens according to claim 1, wherein assuming that a
focal length of the imaging lens during focusing on an object at
infinity is f, a focal length of a j-th lens from the object side
in the second lens group is f2j, and an Abbe number of the j-th
lens from the object side in the second lens group at the d line is
v2j, Conditional Expression (5) is satisfied, which is represented
by - 0.05 < f .times. j = 1 3 1 f 2 j .times. v 2 j < - 0.005
. ( 5 ) ##EQU00009##
6. The imaging lens according to claim 1, wherein the first lens
group consists of, in order from the object side, a first-A
sub-lens group having a positive refractive power, the first-B
sub-lens group, and a first-C sub-lens group having a positive
refractive power.
7. The imaging lens according to claim 6, wherein the first-A
sub-lens group consists of one or two lenses.
8. The imaging lens according to claim 6, wherein the first-C
sub-lens group consists of one or two lenses.
9. The imaging lens according to claim 1, wherein the b1 lens and
the b2 lens are cemented with each other.
10. The imaging lens according to claim 1, wherein the b3 lens and
the b4 lens are cemented with each other.
11. The imaging lens according to claim 1, wherein the positive
lens of the second lens group is a biconvex lens.
12. The imaging lens according to claim 1, wherein Conditional
Expression (1-1) is satisfied, which is represented by
0.12<Db12/DG1<0.22 (1-1).
13. The imaging lens according to claim 1, wherein Conditional
Expression (2-1) is satisfied, which is represented by - 0.01 <
Y max .times. i = 1 k ( 1 Nif - 1 Nir ) / sRi < 0.07 . ( 2 - 1 )
##EQU00010##
14. The imaging lens according to claim 1, wherein Conditional
Expression (3-1) is satisfied, which is represented by
-0.2<(Rb2r+Rb3f)/(Rb2r-Rb3f)<0.1 (3-1).
15. The imaging lens according to claim 4, wherein Conditional
Expression (4-1) is satisfied, which is represented by
-0.6<f/f2<0.2 (4-1).
16. The imaging lens according to claim 5, wherein Conditional
Expression (5-1) is satisfied, which is represented by - 0.035 <
f .times. j = 1 3 1 f 2 j .times. v 2 j < - 0.01 . ( 5 - 1 )
##EQU00011##
17. The imaging lens according to claim 2, wherein Conditional
Expression (6-1) is satisfied, which is represented by
-0.75<(Rb3f-PRb3r)/(Rb3f-Rb3r)<-0.05 (6-1).
18. The imaging lens according to claim 3, wherein Conditional
Expression (7-1) is satisfied, which is represented by
0.35<(Rb2f-PRb2r)/(Rb2f-Rb2r)<1.2 (7-1).
19. An imaging apparatus comprising the imaging lens according to
claim 1.
20. An imaging apparatus comprising the imaging lens according to
claim 2.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Continuation of PCT
International Application No. PCT/JP2018/008425 filed on Mar. 5,
2018, which claims priority under 35 U.S.C. .sctn. 119(a) to
Japanese Patent Application No. 2017-049840 filed on Mar. 15, 2017.
Each of the above applications is hereby expressly incorporated by
reference in its entirety, into the present application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to an imaging lens and an
imaging apparatus. In particular, the present invention relates to
an imaging lens, which is suitable for a factory automation (FA)
camera, a machine vision (MV) camera, a digital camera, a
surveillance camera, an on-board camera, and the like, and an
imaging apparatus comprising the imaging lens.
2. Description of the Related Art
[0003] Examples of the imaging lens having a focusing function
conventionally known include imaging lenses described in
JP2013-178365A, JP2013-210604A, and JP2013-231941A. JP2013-178365A,
JP2013-210604A, and JP2013-231941A each describe a lens system that
consists of a first lens group having a positive refractive power
and a second lens group having a positive or negative refractive
power in order from the object side and that performs focusing by
moving at least the first lens group.
SUMMARY OF THE INVENTION
[0004] There is a demand for the MV camera to capture images of
various shaped objects at various object distances, and there is a
recent demand for the MV camera to be compatible with an imaging
element in which the number of pixels is increased. Therefore, it
is desirable that the imaging lens has high optical performance by
satisfactorily correcting aberrations in the entire imaging range,
in particular, has small fluctuation in astigmatism during focusing
and has small field curvature.
[0005] However, the lens systems described in JP2013-178365A and
JP2013-210604A each have a disadvantage that field curvature is
large. The lens system described in JP2013-231941A has a
disadvantage that fluctuation in astigmatism during focusing is
large.
[0006] The present invention has been made in consideration of the
above-mentioned situations, and it is possible to provide an
imaging lens, which has a small field curvature and has favorable
optical performance by suppressing fluctuation in astigmatism
during focusing, and an imaging apparatus comprising the imaging
lens.
[0007] An imaging lens of the present invention consists of, in
order from an object side: a first lens group that moves toward the
object side during focusing from a distant object to a close-range
object and has a positive refractive power; and a second lens group
that remains stationary with respect to an image plane during
focusing. The first lens group has a first-B sub-lens group
including an aperture stop in an inside thereof. The first-B
sub-lens group consists of, in order from the object side, a b1
lens which is a positive lens, a b2 lens which is a negative lens
concave toward an image side, an aperture stop, a b3 lens which is
a negative lens concave toward the object side, and a b4 lens which
is a positive lens. The second lens group consists of, in order
from the object side, a negative lens, a positive lens, and a
negative lens. In addition, assuming that a distance on an optical
axis from an object side surface of the b1 lens to an image side
surface of the b2 lens is Db12, a distance on the optical axis from
a surface closest to the object side in the first lens group to a
surface closest to the image side in the first lens group is DG1, a
maximum image height is Ymax, a total number of lens surfaces of
the second lens group is k, a refractive index of a medium, which
forms an i-th lens surface from the object side in the second lens
group, on the object side at a d line is Nif, a refractive index of
the medium, which forms the i-th lens surface from the object side
in the second lens group, on the image side at the d line is Nir,
and a radius of curvature of the i-th lens surface from the object
side in the second lens group is sRi, Conditional Expressions (1)
and (2) are satisfied.
0.1 < Db 12 / DG 1 < 0.25 ( 1 ) - 0.02 < Y max .times. i =
1 k ( 1 Nif - 1 Nir ) / sRi < 0.08 ( 2 ) ##EQU00001##
[0008] It is preferable that the imaging lens of the present
invention satisfies Conditional Expression (1-1) and/or (2-1).
0.12 < Db 12 / DG 1 < 0.22 ( 1 - 1 ) - 0.01 < Y max
.times. i = 1 k ( 1 Nif - 1 Nir ) / sRi < 0.07 ( 2 - 1 )
##EQU00002##
[0009] In the imaging lens of the present invention, assuming that
a radius of curvature of the image side surface of the b2 lens is
Rb2r, and a radius of curvature of an object side surface of the b3
lens is Rb3f, it is preferable to satisfy Conditional Expression
(3), and it is more preferable to satisfy Conditional Expression
(3-1).
-0.3<(Rb2r+Rb3f)/(Rb2r-Rb3f)<0.3 (3)
-0.2<(Rb2r+Rb3f)/(Rb2r-Rb3f)<0.1 (3-1)
[0010] In the imaging lens of the present invention, assuming that
a focal length of a whole system during focusing on an object at
infinity is f, and a focal length of the second lens group is f2,
it is preferable to satisfy Conditional Expression (4), and it is
more preferable to satisfy Conditional Expression (4-1).
-0.7<f/f2<0.3 (4)
-0.6<f/f2<0.2 (4-1)
[0011] In the imaging lens of the present invention, assuming that
a focal length of a whole system during focusing on an object at
infinity is f, a focal length of a j-th lens from the object side
in the second lens group is f2j, and an Abbe number of the j-th
lens from the object side in the second lens group at the d line is
v2j, it is preferable to satisfy Conditional Expression (5), and it
is more preferable to satisfy Conditional Expression (5-1).
- 0.05 < f .times. j = 1 3 1 f 2 j .times. v 2 j < - 0.005 (
5 ) - 0.035 < f .times. j = 1 3 1 f 2 j .times. v 2 j < -
0.01 ( 5 - 1 ) ##EQU00003##
[0012] In the imaging lens of the present invention, assuming that
a radius of curvature of an object side surface of the b3 lens is
Rb3f, and a radius of curvature of an image side surface of the b3
lens is Rb3r, it is preferable to satisfy Conditional Expression
(6), and it is more preferable to satisfy Conditional Expression
(6-1).
-0.8<(Rb3f+Rb3r)/(Rb3f-Rb3r)<0 (6)
-0.75<(Rb3f+Rb3r)/(Rb3f-Rb3r)<-0.05 (6-1)
[0013] In the imaging lens of the present invention, assuming that
a radius of curvature of an object side surface of the b2 lens is
Rb2f, and a radius of curvature of the image side surface of the b2
lens is Rb2r, it is preferable to satisfy Conditional Expression
(7), and it is more preferable to satisfy Conditional Expression
(7-1).
0.3<(Rb2f+Rb2r)/(Rb2f-Rb2r)<1.5 (7)
0.35<(Rb2f+Rb2r)/(Rb2f-Rb2r)<1.2 (7-1)
[0014] In the imaging lens of the present invention, it is
preferable that the first lens group consists of, in order from the
object side, a first-A sub-lens group having a positive refractive
power, a first-B sub-lens group, and a first-C sub-lens group
having a positive refractive power. In this case, it is preferable
that the first-A sub-lens group consists of one or two lenses.
Further, it is preferable that the first-C sub-lens group consists
of one or two lenses.
[0015] In the imaging lens of the present invention, it is
preferable that the b1 lens and the b2 lens are cemented with each
other. Further, it is preferable that the b3 lens and the b4 lens
are cemented with each other.
[0016] In the imaging lens of the present invention, it is
preferable that the positive lens of the second lens group is a
biconvex lens.
[0017] An imaging apparatus of the present invention comprises the
imaging lens of the present invention.
[0018] In the present description, it should be noted that the
terms "consisting of .about." and "consists of .about." mean that
the imaging lens may include not only the above-mentioned elements
but also lenses substantially having no powers, optical elements,
which are not lenses, such as a stop, a filter, and a cover glass,
and mechanism parts such as a lens flange, a lens barrel, an
imaging element, and/or a camera shaking correction mechanism.
[0019] In addition, the term ".about. group that has a positive
refractive power" in the present specification means that the group
has a positive refractive power as a whole. It is the same for the
term ".about. group that has a negative refractive power". The
".about. lens group" is not necessarily composed of a plurality of
lenses, but may be composed of only one lens. The sign of the
refractive power of the above defined lens group, the sign of the
refractive power of the lens, the surface shape of the lens, and
the radius of curvature are assumed as those in the paraxial region
in a case where the aspheric surface is included therein. The
"negative meniscus lens" is a meniscus lens that has a negative
refractive power. All the conditional expressions are based on the
d line (a wavelength of 587.6 nm (nanometers)) in a state where the
object at infinity is in focus. In a case of calculating
Conditional Expressions (2) and (2-1), the cemented surface is
counted as one surface.
[0020] According to the present invention, the lens system consists
of, in order from the object side, a positive first lens group that
moves to the object side during focusing from the distant object to
the close-range object, and a second lens group that does not move
during focusing. In the lens system, by appropriately setting
specific configurations of the first lens group and the second lens
group, predetermined conditional expressions are satisfied. With
such a configuration, it is possible to provide an imaging lens,
which has a small field curvature and has favorable optical
performance by suppressing fluctuation in astigmatism during
focusing, and an imaging apparatus comprising the imaging lens.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a cross-sectional view illustrating a
configuration and an optical path of an imaging lens of Example 1
of the present invention.
[0022] FIG. 2 is a cross-sectional view illustrating a
configuration and an optical path of an imaging lens of Example 2
of the present invention.
[0023] FIG. 3 is a cross-sectional view illustrating a
configuration and an optical path of an imaging lens of Example 3
of the present invention.
[0024] FIG. 4 is a cross-sectional view illustrating a
configuration and an optical path of an imaging lens of Example 4
of the present invention.
[0025] FIG. 5 is a cross-sectional view illustrating a
configuration and an optical path of an imaging lens of Example 5
of the present invention.
[0026] FIG. 6 is a cross-sectional view illustrating a
configuration and an optical path of an imaging lens of Example 6
of the present invention.
[0027] FIG. 7 is a diagram of aberrations of the imaging lens of
Example 1 of the present invention, where the diagram includes
spherical aberration diagram, astigmatism diagram, distortion
diagram, and lateral chromatic aberration diagram, in order from
the left side thereof.
[0028] FIG. 8 is a diagram of aberrations of the imaging lens of
Example 2 of the present invention, where the diagram includes
spherical aberration diagram, astigmatism diagram, distortion
diagram, and lateral chromatic aberration diagram, in order from
the left side thereof.
[0029] FIG. 9 is a diagram of aberrations of the imaging lens of
Example 3 of the present invention, where the diagram includes
spherical aberration diagram, astigmatism diagram, distortion
diagram, and lateral chromatic aberration diagram, in order from
the left side thereof.
[0030] FIG. 10 is a diagram of aberrations of the imaging lens of
Example 4 of the present invention, where the diagram includes
spherical aberration diagram, astigmatism diagram, distortion
diagram, and lateral chromatic aberration diagram, in order from
the left side thereof.
[0031] FIG. 11 is a diagram of aberrations of the imaging lens of
Example 5 of the present invention, where the diagram includes
spherical aberration diagram, astigmatism diagram, distortion
diagram, and lateral chromatic aberration diagram, in order from
the left side thereof.
[0032] FIG. 12 is a diagram of aberrations of the imaging lens of
Example 6 of the present invention, where the diagram includes
spherical aberration diagram, astigmatism diagram, distortion
diagram, and lateral chromatic aberration diagram, in order from
the left side thereof.
[0033] FIG. 13 is a schematic configuration diagram of an imaging
apparatus according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Hereinafter, embodiments of the present invention will be
described in detail with reference to the drawings. FIGS. 1 to 6
are cross-sectional views illustrating configurations and optical
paths of imaging lenses according to an embodiment of the present
invention, and respectively correspond to Examples 1 to 6 to be
described later. Basic configurations and methods shown in the
drawings of examples shown in FIGS. 1 to 6 are the same, and will
be hereinafter described with reference to mainly the example shown
in FIG. 1. FIG. 1 shows the state where the infinite distance
object is in focus, and shows optical paths of on-axis rays 2 and
off-axis rays with the maximum angle of view 3, where the left side
is the object side thereof, and the right side thereof is the image
side.
[0035] This imaging lens is a single focus lens, and consists of a
first lens group G1 and a second lens group G2 in order from the
object side to the image side along the optical axis Z. The first
lens group G1 has an aperture stop St inside. It should be noted
that the aperture stop St shown in FIG. 1 does not necessarily
indicate its size and shape, and indicates a position of the stop
on the optical axis Z.
[0036] In order to apply the imaging lens to an imaging apparatus,
it is preferable to provide various filters and/or a protective
cover glass based on specification of the imaging apparatus. Thus,
FIG. 1 shows an example where a plane-parallel-plate-like optical
member PP, in which those are considered, is disposed between the
lens system and the image plane Sim. However, a position of the
optical member PP is not limited to that shown in FIG. 1, and it is
also possible to adopt a configuration in which the optical member
PP is omitted.
[0037] The first lens group G1 is configured to have a positive
refractive power, and is configured to move to the object side
during focusing from a distant object to a close-range object. The
second lens group G2 is configured to remain stationary with
respect to the image plane Sim during focusing. With such a
configuration, it is possible to suppress fluctuations in spherical
aberration and astigmatism during focusing. In the example shown in
FIG. 1, the entire first lens group G1 is configured to move
integrally during focusing. Thereby, it is possible to simplify a
driving mechanism thereof.
[0038] The first lens group G1 consists of a first-B sub-lens group
G1B including an aperture stop St in the inside thereof. The
first-B sub-lens group consists of, in order from the object side,
a b1 lens Lb1 which is a positive lens, a b2 lens Lb2 which is a
negative lens concave toward the image side, an aperture stop St, a
b3 lens Lb3 which is a negative lens concave toward the object
side, and b4 lens Lb4 which is a positive lens. As described above,
coma aberration can be satisfactorily suppressed by providing the
first-B sub-lens group G1B which is configured to be symmetric to
the aperture stop St. The b1 lens Lb1 is preferably convex toward
the object side, and the b4 lens Lb4 is preferably convex toward
the image side. In such a case, coma aberration can be more
satisfactorily suppressed.
[0039] It is preferable that the b1 lens Lb1 and the b2 lens Lb2 be
cemented to each other. Thereby, there is an advantage in
correcting longitudinal chromatic aberration. Similarly, it is
preferable that the b3 lens Lb3 and the b4 lens Lb4 be cemented to
each other. Thereby, there is an advantage in correcting
longitudinal chromatic aberration.
[0040] The first lens group G1 may have s sub-lens group other than
the first-B sub-lens group G1B. For example, the first lens group
G1 may be configured to consist of, in order from the object side,
a first-A sub-lens group G1A having a positive refractive power, a
first-B sub-lens group G1B, and a first-C sub-lens group G1C having
a positive refractive power. In such a case, coma aberration can be
satisfactorily suppressed.
[0041] In a case where the first lens group G1 consists of the
above three sub-lens groups, it is preferable that the first-A
sub-lens group G1A is configured to consist of one or two lenses.
In such a case, it becomes easy to achieve both suppression of the
entire lens system length and favorable aberration correction. The
first-A sub-lens group G1A in the example of FIGS. 1 and 3 consists
of, in order from the object side, a negative lens and a positive
lens. In a case where the negative lens is disposed to be closest
to the object side in the whole system as described above, there is
an advantage in achieving wide angle. In a case where the first-A
sub-lens group G1A is configured to consist of one positive lens as
in the examples of FIGS. 2 and 4, there is an advantage in
achieving reduction in size. In a case where the first-A sub-lens
group G1A is configured to consist of two positive lenses as in the
examples of FIGS. 5 and 6, there is an advantage in correcting
spherical aberration.
[0042] In a case where the first lens group G1 consists of the
above three sub-lens groups, it is preferable that the first-C
sub-lens group G1C be configured to consist of one or two lenses.
In such a case, it becomes easy to achieve both suppression of the
entire lens system length and favorable aberration correction. The
first-C sub-lens group G1C in the example of FIGS. 1, 3, 5, and 6
consists of two positive lenses. The first-C sub-lens group G1C in
the example of FIGS. 2 and 4 consists of one positive lens.
[0043] The second lens group G2 consists of, in order from the
object side, a lens L21 which is a negative lens, a lens L22 which
is a positive lens, and a lens L23 which is a negative lens.
Thereby, it is possible to satisfactorily suppress fluctuation in
astigmatism during focusing while achieving reduction in size with
a relatively small number of lenses.
[0044] It is preferable that the positive lens in the second lens
group G2 is a biconvex lens. In such a case, it becomes easy to
balance spherical aberration and distortion.
[0045] The three lenses composing the second lens group G2 can have
various aspects. In the example of FIG. 1, the lens L22 and the
lens L23 are cemented with each other. Thereby, there is an
advantage in correcting lateral chromatic aberration. In the
examples of FIGS. 3 and 5, the lens L21 and the lens L22 are
cemented with each other. Thereby, there is an advantage in
correcting longitudinal chromatic aberration. The lens L21 in the
example of FIG. 2 is a negative meniscus lens concave toward the
object side. Thereby, there is an advantage in correcting spherical
aberration. In the examples of FIGS. 4 and 6, the air gap between
the lens L21 and the lens L22 and the air gap between the lens L22
and the lens L23 are set to be large. Thereby, there is an
advantage in correcting coma aberration.
[0046] Next, a configuration relating to Conditional Expression of
the imaging lens of the present embodiment will be described.
Assuming that a distance on the optical axis from an object side
surface of the b1 lens Lb1 to an image side surface of the b2 lens
Lb2 is Db12 and a distance on the optical axis from a surface
closest to the object side in the first lens group G1 to a surface
closest to the image side in the first lens group G1 is DG1, this
imaging lens is configured to satisfy Conditional Expression (1).
By not allowing the result of Conditional Expression (1) to be
equal to or less than the lower limit, it is possible to
satisfactorily correct field curvature. By not allowing the result
of Conditional Expression (1) to be equal to or greater than the
upper limit, it is possible to prevent the field curvature from
being excessively corrected. In order to enhance the effect
relating to Conditional Expression (1), it is preferable that
Conditional Expression (1-1) is satisfied.
0.1<Db12/DG1<0.25 (1)
0.12<Db12/DG1<0.22 (1-1)
[0047] Further, assuming that a maximum image height is Ymax, a
total number of lens surfaces of the second lens group G2 is k, a
refractive index of a medium, which forms an i-th lens surface from
the object side in the second lens group G2 in a case where i is a
natural number of 1 or more, on the object side at a d line is Nif,
a refractive index of the medium, which forms the i-th lens surface
from the object side in the second lens group G2, on the image side
at the d line is Nir, and a radius of curvature of the i-th lens
surface from the object side in the second lens group G2 is sRi,
this imaging lens is configured to satisfy Conditional Expression
(2). Conditional expression (2) relates to the Petzval sum of the
lens surface of the second lens group G2. By making a configuration
so as to satisfy the range of Conditional Expression (2), it is
possible to suppress fluctuation in astigmatism during focusing. In
order to enhance the effect relating to Conditional Expression (2),
it is preferable that Conditional Expression (2-1) is
satisfied.
- 0.02 < Y max .times. i = 1 k ( 1 Nif - 1 Nir ) / sRi < 0.08
( 2 ) - 0.01 < Y max .times. i = 1 k ( 1 Nif - 1 Nir ) / sRi
< 0.07 ( 2 - 1 ) ##EQU00004##
[0048] Assuming that a radius of curvature of the image side
surface of the b2 lens Lb2 is Rb2r, and a radius of curvature of an
object side surface of the b3 lens Lb3 is Rb3f, it is preferable
that this imaging lens satisfies Conditional Expression (3).
Conditional expression (3) relates to a shape of an air lens formed
by the image side surface of the b2 lens Lb2 and the object side
surface of the b3 lens Lb3. By making a configuration so as to
satisfy the range of conditional expression (3), coma aberration
can be suppressed. In order to enhance the effect relating to
Conditional Expression (3), it is preferable that Conditional
Expression (3-1) is satisfied.
-0.3<(Rb2r+Rb3f)/(Rb2r-Rb3f)<0.3 (3)
-0.2<(Rb2r+Rb3f)/(Rb2r-Rb3f)<0.1 (3-1)
[0049] Further, assuming that a focal length of the whole system
during focusing on the object at infinity is f, and a focal length
of the second lens group G2 is f2, it is preferable that this
imaging lens satisfies Conditional Expression (4). By not allowing
the result of Conditional Expression (4) to be equal to or less
than the lower limit, it is possible to suppress fluctuation in
spherical aberration and astigmatism during focusing. By not
allowing the result of Conditional Expression (4) to be equal to or
greater than the upper limit, it is possible to ensure the
refractive power of the first lens group G1 and to suppress the
amount of movement of the first lens group G1 during focusing. In
order to enhance the effect relating to Conditional Expression (4),
it is preferable that Conditional Expression (4-1) is
satisfied.
-0.7<f/f2<0.3 (4)
-0.6<f/f2<0.2 (4-1)
[0050] Further, assuming that a focal length of the whole system
during focusing on the object at infinity is f, a focal length of a
j-th lens from the object side in the second lens group G2 in a
case where j is an integer of 1 to 3 is f2j, and an Abbe number of
the j-th lens from the object side in the second lens group G2 at
the d line is v2j, it is preferable that this imaging lens
satisfies Conditional Expression (5). By making a configuration so
as to satisfy the range of Conditional Expression (5), it is
possible to suppress fluctuation in lateral chromatic aberration
during focusing. In order to enhance the effect relating to
Conditional Expression (5), it is preferable that Conditional
Expression (5-1) is satisfied.
- 0.05 < f .times. j = 1 3 1 f 2 j .times. v 2 j < - 0.005 (
5 ) - 0.035 < f .times. j = 1 3 1 f 2 j .times. v 2 j < -
0.01 ( 5 - 1 ) ##EQU00005##
[0051] Further, assuming that a radius of curvature of an object
side surface of the b3 lens Lb3 is Rb3f, and a radius of curvature
of an image side surface of the b3 lens Lb3 is Rb3r, it is
preferable that this imaging lens satisfies Conditional Expression
(6). By not allowing the result of Conditional Expression (6) to be
equal to or less than the lower limit, it is possible to prevent
spherical aberration from being excessively corrected. By not
allowing the result of Conditional Expression (6) to be equal to or
greater than the upper limit, there is an advantage in correcting
spherical aberration and suppressing the difference in spherical
aberration for each wavelength. In order to enhance the effect
relating to Conditional Expression (6), it is more preferable that
Conditional Expression (6-1) is satisfied.
-0.8<(Rb3f+Rb3r)/(Rb3f-Rb3r)<0 (6)
-0.75<(Rb3f+Rb3r)/(Rb3f-Rb3r)<-0.05 (6-1)
[0052] Further, assuming that a radius of curvature of an object
side surface of the b2 lens Lb2 is Rb2f, and a radius of curvature
of the image side surface of the b2 lens Lb2 is Rb2r, it is
preferable that this imaging lens satisfies Conditional Expression
(7). By not allowing the result of Conditional Expression (7) to be
equal to or less than the lower limit, there is an advantage in
correcting spherical aberration and suppressing the difference in
spherical aberration for each wavelength. By not allowing the
result of Conditional Expression (7) to be equal to or greater than
the upper limit, it is possible to prevent spherical aberration
from being excessively corrected. In order to enhance the effect
relating to Conditional Expression (7), it is more preferable that
Conditional Expression (7-1) is satisfied.
0.3<(Rb2f+Rb2r)/(Rb2f-Rb2r)<1.5 (7)
0.35<(Rb2f+Rb2r)/(Rb2f-Rb2r)<1.2 (7-1)
[0053] The above-mentioned preferred configurations and/or
available configurations may be optional combinations, and it is
preferable to selectively adopt the configurations in accordance
with required specification. According to the present embodiment,
it is possible to realize an imaging lens having a small field
curvature and favorable optical performance by suppressing
fluctuation in astigmatism during focusing.
[0054] Next, numerical examples of the imaging lens of the present
invention will be described.
Example 1
[0055] A lens configuration of an imaging lens of Example 1 is
shown in FIG. 1, and a configuration and a method thereof shown in
the drawing is as described above. Therefore, repeated description
is partially omitted herein. The imaging lens of Example 1 consists
of, in order from the object side, a first lens group G1 having a
positive refractive power, and a second lens group G2 having a
positive refractive power. During focusing from the object at
infinity to the close-range object, the entire first lens group G1
integrally moves from the image side to the object side, and the
second lens group G2 remains stationary with respect to the image
plane Sim. The first lens group G1 consists of, in order from the
object side, a first-A sub-lens group G1A having a positive
refractive power, a first-B sub-lens group G1B, and a first-C
sub-lens group G1C having a positive refractive power. The first-A
sub-lens group G1A consists of two lenses La1 and La2 in order from
the object side. The first-B sub-lens group G1B consists of, in
order from the object side, a b1 lens Lb1, a b2 lens Lb2, an
aperture stop St, a b3 lens Lb3, and a b4 lens Lb4. The first-C
sub-lens group G1C consists of two lenses Lc1 and Lc2 in order from
the object side. The second lens group G2 consists of three lenses
L21 to L23 in order from the object side. The schematic
configuration of the imaging lens of Example 1 is as described
above.
[0056] Table 1 shows basic lens data of the imaging lens of Example
1, and Table 2 shows specification and variable surface distances.
In Table 1, R is the radius of curvature of each surface, D is the
surface distance, Nd is the refractive index at the d line (a
wavelength of 587.6 nm (nanometers)), and vd is the Abbe number
based on the d line. Here, reference signs of radii of curvature of
surface shapes convex toward the object side are set to be
positive, and reference signs of radii of curvature of surface
shapes convex toward the image side are set to be negative. Table 1
additionally shows the aperture stop St and the optical member PP.
In Table 1, in a place of a surface number of a surface
corresponding to the aperture stop St, the surface number and a
term of (St) are noted. A value at the bottom place of D indicates
a distance between the image plane Sim and the surface closest to
the image side in the table. In Table 1, the variable surface
distances, which are variable during focusing, are referenced by
the reference signs DD[ ], and are written into places of D, where
object side surface numbers of spacings are noted in [ ].
[0057] In Table 2, the values of the focal length f of the whole
system bringing the object at infinity into focus, the focal length
near of the whole system bringing the object at an object distance
of 0.2 m (meters) into focus, the F number FNo, the maximum total
angle of view 2.omega., and the variable surface distance are shown
based on the d line. (.degree.) in the place of 2.omega. indicates
that the unit thereof is a degree. In Table 2, the column denoted
by"Infinity" shows respective values thereof in a state where the
object at infinity is in focus, and the column denoted by "0.2 m"
shows respective values thereof in a state where the object at the
object distance of 0.2 m is in focus.
[0058] In data of each table, a degree is used as a unit of an
angle, and mm (millimeter) is used as a unit of a length, but
appropriate different units may be used since the optical system
can be used even in a case where the system is enlarged or reduced
in proportion. Further, each of the following tables shows
numerical values rounded off to predetermined decimal places.
TABLE-US-00001 TABLE 1 Example 1 Surface Number R D Nd vd 1
80.49545 1.000 1.77250 49.60 2 27.66900 21.482 3 50.50962 4.562
1.83481 42.72 4 -125.73063 1.780 5 21.16426 9.795 1.59522 67.73 6
-28.95220 0.810 1.53172 48.84 7 12.96142 5.184 8(St) .infin. 4.414
9 -13.49552 0.800 1.80100 34.97 10 79.02192 6.237 1.59522 67.73 11
-20.16565 0.200 12 -212.84630 3.504 1.65160 58.55 13 -33.02585
0.200 14 82.58302 5.925 1.65160 58.55 15 -42.53843 DD[15] 16
22.68328 5.490 1.84666 23.78 17 17.02745 2.255 18 53.20440 7.000
1.61800 63.33 19 -18.76501 4.869 1.61293 37.00 20 2798710.75014
5.000 21 .infin. 1.000 1.51633 64.14 22 .infin. 6.279
TABLE-US-00002 TABLE 2 Example 1 Infinity 0.2 m f 25.766 -- fnear
-- 26.152 FNo. 1.86 2.06 2.omega.(.degree.) 39.6 37.0 DD[15] 0.100
4.686
[0059] FIG. 7 shows a diagram of aberrations of the imaging lens of
Example 1. FIG. 7 shows spherical aberrations, amounts of sine
condition violation, astigmatisms, distortions, and lateral
chromatic aberrations are shown in order from the left side. In
FIG. 7, a state where an object at infinity is in focus is shown in
the upper part labeled as "infinity", and a state where an object
having an object distance of "0.2 m" is in focus is shown in the
lower part labeled as "0.2 m (meters)". In the spherical aberration
diagram, aberrations at the d line (a wavelength of 587.6 nm
(nanometers)), the C line (a wavelength of 656.3 nm (nanometers)),
the F line (a wavelength of 486.1 nm (nanometers)), and the g line
(a wavelength of 435.8 nm (nanometers)) are respectively indicated
by the black solid line, the long dashed line, the short dashed
line, and the chain double-dashed line. In the astigmatism diagram,
aberration in the sagittal direction at the d line is indicated by
the solid line, and aberration in the tangential direction at the d
line is indicated by the short dashed line. In the distortion
diagram, aberration at the d line is indicated by the solid line.
In the lateral chromatic aberration, aberrations at the C line, the
F line, and the g line are respectively indicated by the long
dashed line, the short dashed line, and the chain double-dashed
line. In the spherical aberration diagram, FNo. indicates an F
number. In the other aberration diagrams, w indicates a half angle
of view.
[0060] In the description of Example 1, reference signs, meanings,
and description methods of the respective data pieces are the same
as those in the following examples unless otherwise noted.
Therefore, in the following description, repeated description will
be omitted.
Example 2
[0061] FIG. 2 shows a lens configuration of the imaging lens of
Example 2. The schematic configuration of the imaging lens of
Example 2 is the same as that of Example 1 except that the first-A
sub-lens group G1A consists of one lens La1 and the first-C
sub-lens group G1C consists of one lens Lc1. Table 3 shows basic
lens data of the imaging lens of Example 2, Table 4 shows
specification and variable surface distances, and FIG. 8 shows
aberration diagrams thereof.
TABLE-US-00003 TABLE 3 Example 2 Surface Number R D Nd vd 1
34.68409 2.659 1.83481 42.72 2 96.72661 0.200 3 18.60318 5.183
1.61800 63.33 4 -53.11140 0.810 1.54072 47.23 5 12.03665 4.547
6(St) .infin. 5.353 7 -14.25088 1.620 1.61293 37.00 8 19.92789
8.000 1.61800 63.33 9 -22.47644 0.200 10 203.35067 3.511 1.83481
42.72 11 -41.27145 DD[11] 12 -17.81903 4.662 1.84666 23.78 13
-20.44061 0.100 14 52.53768 5.570 1.61800 63.33 15 -42.34645 6.070
16 -30.22328 1.000 1.75520 27.51 17 2525252.52525 5.000 18 .infin.
1.000 1.51633 64.14 19 .infin. 6.231
TABLE-US-00004 TABLE 4 Example 2 Infinity 0.2 m f 36.019 -- fnear
-- 37.710 FNo. 1.88 2.24 2.omega.(.degree.) 28.8 24.4 DD[11] 2.790
13.268
Example 3
[0062] FIG. 3 shows a lens configuration of the imaging lens of
Example 3. The schematic configuration of the imaging lens of
Example 3 is the same as that of Example 1 except that the second
lens group G2 has a negative refractive power. Table 5 shows basic
lens data of the imaging lens of Example 3, Table 6 shows
specification and variable surface distances, and FIG. 9 shows
aberration diagrams thereof.
TABLE-US-00005 TABLE 5 Example 3 Surface Number R D Nd vd 1
90.39228 1.000 1.67270 32.10 2 27.11437 15.722 3 33.68542 5.401
1.80000 29.84 4 -232.99734 2.194 5 21.30913 7.260 1.61800 63.33 6
-34.56535 0.800 1.62004 36.26 7 14.03959 7.142 8(St) .infin. 7.481
9 -13.83387 0.800 1.63980 34.47 10 72.48789 7.398 1.61800 63.33 11
-21.80272 0.200 12 -264.07626 3.762 1.65160 58.55 13 -37.16619
0.200 14 76.83307 8.552 1.65160 58.55 15 -85.69829 DD[15] 16
267.06657 7.010 1.51680 64.20 17 32.62510 7.000 1.61800 63.33 18
-41.27857 3.364 19 -32.59003 1.000 1.91082 35.25 20 -426.72108
5.000 21 .infin. 1.000 1.51633 64.14 22 .infin. 6.295
TABLE-US-00006 TABLE 6 Example 3 Infinity 0.2 m f 34.489 -- fnear
-- 33.716 FNo. 1.85 2.11 2.omega.(.degree.) 30.0 27.8 DD[15] 1.779
8.119
Example 4
[0063] FIG. 4 shows a lens configuration of the imaging lens of
Example 4. The schematic configuration of the imaging lens of
Example 4 is the same as that of Example 1 except that the second
lens group G2 has a negative refractive power and the first-A
sub-lens group G1A consists of one lens La1 and the first-C
sub-lens group G1C consists of one lens Lc1. Table 7 shows basic
lens data of the imaging lens of Example 4, Table 8 shows
specification and variable surface distances, and FIG. 10 shows
aberration diagrams thereof.
TABLE-US-00007 TABLE 7 Example 4 Surface Number R D Nd vd 1
31.58357 4.283 1.77250 49.60 2 177.00608 0.200 3 17.68049 4.135
1.61800 63.33 4 139.41731 0.810 1.58144 40.75 5 12.64057 3.960
6(St) .infin. 6.622 7 -18.91744 0.810 1.60342 38.03 8 21.15389
5.846 1.61800 63.33 9 -26.72950 0.200 10 364.10127 2.871 1.85026
32.27 11 -57.09427 DD[11] 12 -96.19095 1.000 1.51742 52.43 13
24.56826 8.855 14 25.90085 6.874 1.61800 63.33 15 -34.66855 5.437
16 -22.50359 1.000 1.51742 52.43 17 -3450517.22686 5.000 18 .infin.
1.000 1.51633 64.14 19 .infin. 6.356
TABLE-US-00008 TABLE 8 Example 4 Infinity 0.2 m f 48.512 -- fnear
-- 48.386 FNo. 2.44 3.10 2.omega.(.degree.) 21.6 16.8 DD[11] 0.100
12.677
Example 5
[0064] FIG. 5 shows a lens configuration of the imaging lens of
Example 5. The schematic configuration of the imaging lens of
Example 5 is the same as that of Example 1. Table 9 shows basic
lens data of the imaging lens of Example 5, Table 10 shows
specification and variable surface distances, and FIG. 11 shows
aberration diagrams thereof.
TABLE-US-00009 TABLE 9 Example 5 Surface Number R D Nd vd 1
196.68312 8.000 1.84666 23.78 2 231.74740 10.114 3 36.79526 3.406
1.65160 58.55 4 96.97495 0.100 5 21.26741 6.059 1.61800 63.33 6
-74.59290 0.810 1.53172 48.84 7 14.04541 6.280 8(St) .infin. 7.135
9 -16.73696 0.870 1.56732 42.82 10 26.82531 10.000 1.61800 63.33 11
-26.02106 0.200 12 -548.42711 3.021 1.65160 58.55 13 -55.25956
0.200 14 491.08260 10.000 1.65160 58.55 15 -119.76110 DD[15] 16
-131.93625 5.395 1.59551 39.24 17 27.23360 7.000 1.83481 42.72 18
-56.44266 5.227 19 -34.56818 1.000 1.69895 30.13 20 2777777.77780
5.000 21 1.000 1.51633 64.14 22 6.328
TABLE-US-00010 TABLE 10 Example 5 Infinity 0.2 m f 48.515 -- fnear
-- 49.270 FNo. 2.02 2.78 2.omega.(.degree.) 21.6 17.4 DD[15] 3.219
20.288
Example 6
[0065] FIG. 6 shows a lens configuration of the imaging lens of
Example 6. The schematic configuration of the imaging lens of
Example 6 is the same as that of Example 1 except that the second
lens group G2 has a negative refractive power. Table 11 shows basic
lens data of the imaging lens of Example 6, Table 12 shows
specification and variable surface distances, and FIG. 12 shows
aberration diagrams thereof.
TABLE-US-00011 TABLE 11 Example 6 Surface Number R D Nd vd 1
81.13544 2.160 1.51680 64.20 2 179.04208 0.200 3 46.96191 3.104
1.48749 70.24 4 150.89626 8.667 5 23.89978 5.740 1.59522 67.73 6
-63.16465 0.800 1.51680 64.20 7 16.22957 4.210 8(St) .infin. 10.457
9 -18.84784 0.810 1.54814 45.78 10 27.45218 6.814 1.59522 67.73 11
-28.03959 0.200 12 -500.88226 3.064 1.48749 70.24 13 -53.29564
6.011 14 -606.83460 3.069 1.48749 70.24 15 -54.36419 DD[15] 16
-274.92257 5.047 1.84666 23.78 17 36.72507 7.240 18 39.45725 5.512
1.76182 26.52 19 -64.14717 12.150 20 -33.51306 1.000 1.60342 38.03
21 2655633.20542 5.000 22 .infin. 1.000 1.51633 64.14 23 .infin.
6.338
TABLE-US-00012 TABLE 12 Example 6 Infinity 0.2 m f 73.508 -- fnear
-- 58.968 FNo. 2.87 4.11 2.omega.(.degree.) 14.2 10.6 DD[15] 1.806
27.561
[0066] Table 13 shows values corresponding to Conditional
Expressions (1) to (7) relating to the imaging lenses of Examples 1
to 6. The values shown in Table 13 are based on the d line.
TABLE-US-00013 TABLE 13 Expression Number Example 1 Example 2
Example 3 Example 4 Example 5 Example 6 (1) Db12/DG1 0.189 0.211
0.146 0.185 0.130 0.152 (2) Ymax .times. .SIGMA.(1/Nif - 1/Nir)/sRi
-0.005 0.011 0.025 0.060 0.032 0.068 (3) (Rb2r + Rb3f)/(Rb2r -
-0.020 -0.084 0.007 -0.199 -0.087 -0.075 Rb3f) (4) f/f2 0.100 0.182
-0.131 -0.009 0.049 -0.598 (5) f .times. .SIGMA.(1/(f2j .times.
.nu.2j)) -0.013 -O.020 -0.015 -O.015 -0.016 -O.032 (6) (Rb3f +
Rb3r)/(Rb3f - Rb3r) -O.708 -0.166 -0.679 -0.056 -0.232 -0.186 (7)
(Rb2f + Rb2r)/(Rb2f - Rb2r) 0.382 0.630 0.422 1.199 0.683 0.591
[0067] As can be seen from the above data, in the imaging lenses of
Examples 1 to 6, fluctuation in astigmatism during focusing is
suppressed, field curvature is small, each aberration is
satisfactorily corrected, and thus high optical performance is
realized. Further, the imaging lenses of Examples 1 to 6 each have
a total angle of view of 45.degree. or less, and each are a lens
system suitable as a telephoto type.
[0068] Next, an imaging apparatus according to an embodiment of the
present invention will be described. FIG. 13 is a schematic
configuration diagram of an imaging apparatus 10 using the imaging
lens 1 according to the above-mentioned embodiment of the present
invention as an example of an imaging apparatus of an embodiment of
the present invention. As the imaging apparatus 10, for example,
there is an FA camera, an MV camera, or a surveillance camera.
[0069] The imaging apparatus 10 comprises: the imaging lens 1; a
filter 4 that is disposed on the image side in the imaging lens 1;
an imaging element 5; a signal processing section 6 that performs
processing of calculating a signal which is output from the imaging
element 5, and a focus control section 7 that is for performing
focusing of the imaging lens 1. FIG. 13 schematically shows the
first lens group G1 and the second lens group G2 which are
belonging to the imaging lens 1. The imaging element 5 captures an
image of a subject, which is formed through the imaging lens 1, and
converts the image into an electrical signal. For example, charge
coupled device (CCD), complementary metal oxide semiconductor
(CMOS), or the like may be used. The imaging element 5 is disposed
such that the imaging surface thereof is coplanar with the image
plane of the imaging lens 1. The imaging apparatus 10 of the
present embodiment comprises the imaging lens 1. Thus, it is
possible to appropriately cope with a change in object distance,
and it is possible to acquire a favorable image.
[0070] The present invention has been hitherto described through
embodiments and examples, but the present invention is not limited
to the above-mentioned embodiments and examples, and may be
modified into various forms. For example, values such as the radius
of curvature, the surface distance, the refractive index, and the
Abbe number of each lens are not limited to the values shown in the
numerical examples, and different values may be used therefor.
[0071] For example, in each example, the lens system, which
performs focusing from the object at infinity to the close-range
object, is used. However, it is needless to say that the present
invention can be applied to an imaging lens which performs focusing
from a distant object at a finite distance to a close-range
object.
[0072] The imaging apparatus according to the above-mentioned
embodiment of the present invention is not limited to the
above-mentioned examples, and may be modified into various forms
such as a digital camera and an in-vehicle camera.
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